The present invention relates to an ultrasound diagnostic apparatus and a data processing method for creating and displaying an ultrasound image of a diagnostic region of a subject using an ultrasonic wave.
An ultrasound diagnostic apparatus using an ultrasound image has hitherto been put into practical use in the field of medicine. In general, the ultrasound diagnostic apparatus has an ultrasound probe in which a transducer array is installed, and an apparatus body connected to the ultrasound probe. In the ultrasound diagnostic apparatus, an ultrasonic beam is transmitted from the ultrasound probe toward a subject, an ultrasonic echo, which is a reflected ultrasonic beam from the subject, is received by the ultrasound probe to acquire a reception signal, and the acquired reception signal is electrically processed by the apparatus body to produce an ultrasound image.
In the conventional ultrasound diagnostic apparatus, the value of the sound speed of ultrasonic wave set for the entire apparatus is fixed to a certain value assuming that the sound speed of ultrasonic wave in the living body of the subject is constant.
However, since the sound speed changes depending on differences in tissues such as a fat layer and a muscular layer in the living body, the sound speed of ultrasonic wave in the subject (hereinafter, referred to as an ambient sound speed) is not uniform. In addition, since the thickness of the fat layer or the muscular layer is different between a fat subject and a thin subject, there are individual differences in the ambient sound speed for each subject.
As described above, in the conventional ultrasound diagnostic apparatus, the sound speed of ultrasonic wave set for the entire apparatus (hereinafter, referred to as a set sound speed) is fixed to a certain value. In this case, the more the ambient sound speed, which is the sound speed in the subject, deviates from the set sound speed, the more the arrival time of the reflected wave (ultrasonic echo) deviates from the delay time set for the ultrasonic wave transmission/reception circuit. For this reason, there has been a problem in that the focusing is degraded, and accordingly, the quality of the obtained ultrasound image is degraded.
In contrast, as shown in FIG. 8, the first embodiment described in JP 2009-142680 A discloses an ultrasound diagnostic apparatus which includes an ultrasonic wave transmitter/receiver 2 that drives a probe 1 to transmit ultrasonic waves to a subject and processes signals of the reflected echo from the subject, a phasing adder 3 that aligns the phases of the reception signals processed by the ultrasonic wave transmitter/receiver 2, and an image display unit 4 that displays the signals from the phasing adder 3 as an image, and in the ultrasound diagnostic apparatus, a plurality of values of switching interval of the optimal reception wave delay correction value are stored in advance in a focus switching interval storage unit 7 for each observation region or each physique of the subject, a focus switching interval instruction unit 8 sets an arbitrary switching interval of reception wave delay correction value in the focus switching interval storage unit 7, and the phasing adder 3 adjusts the focus according to the set switching interval of reception wave delay correction value.